Materials

If civilization still exists on planet earth in a billion years, what materials can it use?

Lasting civilizations can use only materials

1. that form closed cycles or loops (such as carbon, water, oxygen, hydrogen, hydrocarbons, nitrogen), or
2. that can be regained from the environment economically to form forced cycle before they reach harmful concentrations
3. that (if available from outside) can accumulate in ever increasing concentrations in the environment/biosphere without negative effect on life and civilization
4. that exist in the biosphere or can be brought there by economical means

Carbon and hydrocarbon based materials, for which cycles exist in nature, have amazing properties, ranging from diamond, nanotubes and materials that can be turned into semiconductors and transistors or plastics as well as living organisms. Those that nature recycles before dangerous concentrations accumulate could be used indefinitely in civilizations.

For materials such as metals or doted semiconductors no natural cycles are known. Even a modest wear or oxidation of such materials would eventually result in high concentrations in the environment. Lasting civilizations could use such materials only if they posess the possibility to remove these from the environment in concentrations that do no harm, thereby closing cycles technically. For many materials we widely use today, such as aluminum or nickel and maybe even iron, we do not yet posess economical removal technologies from the environment at low concentrations.